This invention relates to a digital filter used for imparting a desired tone color to a tone signal to be produced in an electronic musical instrument.
A tone color imparting circuit in an electronic musical instrument requires subtle circuit characteristics and has in most cases been constructed of an analog circuit. The prior art analog tone color imparting circuit, particularly an analog filter, tends to be of a large size. Particularly, in a case where a tone color having a fixed formant (e.g., human voice, wind instruments such as oboes and basoons, piano and stringed instruments) is to be realized, a large number of analog filter circuits must be provided in parallel resulting in a circuit construction of a large size. Besides, a digital tone signal cannot be applied to the analog tone color circuit directly so that application of a digital tone generation circuit requires an extra process. More specifically, a digital to analog converter must be provided between the digital tone generation circuit and the analog tone color circuit. Such digital to analog converter must be provided for each of channels which require different tone color processings (i.e., filter processings) and, accordingly, a large number of digital to analog converters are required for the entire system.
It is, therefore, an object of this invention to provide a system for imparting a tone color in an electronic musical instrument which is capable of easily realizing a fixed formant with a compact and inexpensive construction and to which a digital tone generation circuit is readily applicable. As a device for meeting such purpose, there is a digital filter. A circuit including a digital filter can be constructed of an LSI. A problem posed by reduction in the size of the LSI circuit is reduction in the number of connecting pins and the number of wirings.
It is therefore another object of the invention to reduce the number of wirings and the number of connecting pins required for supplying digital signals to a digital filter.
As a prior art of an electronic musical instrument incorporating a digital filter, there is U.S. Pat. No. 4,130,043 entitled "Electronic musical instrument having filter-and-delay loop for tone production". Since, however, the digital filter operation in this prior art device is performed in bit-parallel, the construction of the digital filter circuit and its peripheral circuits as well as wirings and connectors tends to become large and complicated. It is therefore another object of the invention to make the circuit construction smaller and simpler by bit-serially performing the operation or process of the digital filter incorporated in the electronic musical instrument.
Filter circuits must generally be provided individually for respective channels which require different filter processings. Provision of the filter circuit for each of the channels necessitates a bulky construction and a high cost of manufacturing. It is therefore still another object of the invention to make hardware of the digital filter compact and economical in a case where filter processings for plural channels are required.